485 Hierarchical species structure is the species list of a biocenose, rearranged according to a decrease in spe cies abundance. This series of numbers is commonly approximated by a simple mathematical model. At present, four models are used to describe the structure of communities: hyperbolic equation, broken stick model, lognormal distribution, and geometric series (Pesenko, 1982). In this work, we provide a theoretical justification for the latter model. The species structure of Pacific salmons (Oncorhynchus) is used as an example.